Several platinum catalyst-containing thermoplastic resin fine particle catalysts are known as curing acceleration catalysts for silicone compositions which cure by a hydrosilation reaction.
For example, U.S. Pat. No. 4,481,341 to Schlak et al., JP (Kokai) 64-47442, JP (Kokai) 64-51140, and U.S. Pat. No. 5,015,691 to Lewis et al., describe platinum catalyst-containing organic thermoplastic resin fine particle catalysts. However, these organic thermoplastic resin fine particle catalysts are inferior in heat resistance. Further, they have some disadvantages in that silicone compositions using them as a curing acceleration catalyst tend to show inferior mechanical properties and discoloration caused when heated for curing or when used at high temperatures after curing.
As a method to solve this problem, it has been proposed to use platinum catalyst-containing thermoplastic silicone resin catalysts. For example, in JP 53-41707 and U.S. Pat. No. 4,481,341, methods have been proposed to obtain a thermoplastic platinum catalyst-containing silicone resin fine particle catalyst by mechanically grinding mixtures of a platinum catalyst and a thermoplastic silicone resin. Although these methods have been effective for relatively low activity platinum catalysts such as 2-ethylhexanol solution of chloroplatinic acid or isopropyl alcohol-modified chloroplatinic acid they have a disadvantage in that they are barely effective to inhibit catalyst activity when applied to high activity platinum catalysts. Furthermore, it has been difficult to obtain fine particle catalysts of less than 10 .mu.m in average particle size by these methods. Therefore, when they are used as a curing acceleration catalyst for the silicone composition, the catalyst diffusion during thermal curing reaction is not sufficient. This results in a problem in that the curing reaction of the silicone composition may not be completed.
EP 0347895 to Togashi et al., U.S. Pat. No. 5,017,654 to Togashi et al. and JP (Kokai) 4-46962 to Saruyama et al. describe thermoplastic silicone resin fine particle catalysts containing high activity platinum catalysts. Specifically, EP 0347895 describes a hydrosilation reaction catalyst for which the thermoplastic resin containing high activity platinum catalyst is pulverized to fine particles, and then the platinum catalyst existing on the surface is removed by washing off, so that the catalyst activity is suppressed. The high activity catalyst is then released by heating. Also, U.S. Pat. No. 5,017,654 and JP (Kokai) 4-46962 describe silicone compositions which cure quickly during thermal curing by the combined use of platinum catalyst-containing thermoplastic silicone resin fine particle catalyst and a particular kind of compound. By these methods, it became possible to manufacture thermosetting silicone compositions featured in that they can be stored stably at room temperature over a long period of time, and quickly complete curing during thermal curing, and yet the essential characteristics of the silicone compositions are not impaired. However, it has been difficult to control the curing rate and the storage stability by these methods. Further, there has been such a problem that the storage stability would be degraded with increasing the curing rate, and the curing rate would be reduced with increasing the storage stability.
It has now been found that when a special thermoplastic silicone resin is used to produce the platinum catalyst-containing thermoplastic silicone fine particle catalyst, it is possible to control the releasing temperature of the platinum catalyst when heated, so that it is possible to control the curing rate and the storage stability.
Therefore, it is an objective of the present invention to present a thermosetting silicone composition which is excellent in storage stability in the vicinity of room temperature, and of which the curing rate is fast when heated.